The present invention relates to clarifiers of a type wherein flow passages are formed between a plurality of inclined plates. The invention is particularly concerned with one or more improvements for facilitating operation of the clarifier in a wide variety of applications while also permitting simplified construction of the clarifier in order to minimize initial cost, reduce the need for complex operating procedures and to facilitate maintenance of the clarifier.
In the past, the most widely used clarifiers or settlers have been in the form of large basins, tanks or the like where the liquid to be clarified is held until one or more selected phases separate because of sedimentation rates or phase separation phenomenon. Generally, large basins or tanks have been employed where liquid to be clarified includes solids which tend to separate under the effects of gravity given a sufficient standing time.
Such basins or similar arrangements are commonly employed in water treatment and sewage disposal facilities, for example. These facilities depend upon relatively long holding periods in order to accomplish separation and are characterized by a requirement for excessive amounts of volume. This need for excessive storage volume and operating space may undesirably affect operating costs, particularly initial installation costs. In addition, many plant facilities which require clarifying or settling operations simply do not have the necessary space for the installation of large settling basins or tanks.
One solution to this problem has been the development of inclined passage clarifiers. Clarifiers of this type are commonly characterized by a number of angled flow passages or channels formed, for example, by a plurality of inclined plates. Liquid flowing between the plates is subject to phase separation under conventional principles of operation. The particular utility of such clarifiers is based upon the well known fact that the depth of a simple gravity settler or clarifier has little, if any, bearing on its effective rate of operation. The most significant value in the design of a gravity settler is its available settling area.
The concept of employing a series of inclined passages in close proximity to each other has been found to be one of the most effective means for increasing the settling area per unit volume while at the same time reducing overall size and cost for a clarifier or settling unit.
With the inclined passage concept, the effective gravity settling area becomes the horizontally projected area of all of the passages. As a result, a very substantial settling area may be made availabe relative to the surface area occupied by the clarifier or settler. Overall flow rates for liquid passing through conventional open settling basins and the like can, in general, be applied to the sizing of inclined plate clarifiers by substituting the "projected area" for the "surface settling area" of the conventional open clarifier. This distinct advantage, made possible by the general configuration of inclined plate clarifiers or settlers, is tending to increase their use in many applications.
Operation of inclined plate clarifiers may be further enhanced in various ways to increase the rate and/or quality of clarification. Such capabilities are of particular importance because of the wide variety of operating conditions which may be encountered and the variety of liquids to be clarified. For example, in some applications, liquids to be clarified may have varying amounts of suspended solids ranging from heavy material tending to settle out very rapidly to light materials which are difficult to separate and may in some instances require the use of flocculating agents. Liquids to be clarified may require the removal of a relatively low density phase such as oils suspended in water. The liquid may either be aqueous or nonaqueous and, in some instances, may include both solids subject to settling under the effects of gravity as well as one or more low density phases which must be separated in order to produce a clarified liquid of satisfactory quality.
The prior art includes numerous examples of various inclined passage clarifiers or settlers for treating one or more liquids of the type discussed above. For example, it is known in the prior art that, under certain conditions, it is preferable to employ an "upflow" mode of operation wherein the liquid to be clarified is introduced adjacent the bottoms of the inclined passages wiht clarified liquid being removed at some point toward the top of the clarifier.
Under other conditions, it has been found preferable to employ a "downflow" mode of operation wherein the liquid to be clarified is introduced at the top of the clarifier or settler with the clarified liquid being removed from a lower portion of the clarifier.
Numerous other modifications have been developed within such inclined passage clarifiers or settlers to further enhance clarification of liquids in various applications. However, it has commonly been the case that the clarifier or settler must be uniquely tailored to the particular application where the clarifier is being used. Accordingly, the cost of designing and installing the clarifiers has tended to be substantial. For the same reasons, operating procedures for such clarifiers have tended to vary widely in different applications and under different operating conditions.
Another problem particularly contemplated by the present invention concerns the removal of low density liquids or solids from a liquid to be clarified. The most common example of this would be an aqueous liquid including oils or possibly low density petroleum solids. Such a situation commonly arises in various waste waters or due to accidental spills caused by the rupture of oil lines or the like. Because of constantly changing environmental criteria which may permit only a few parts per million of such impurities in the effluent, it is necessary to provide more efficient and economical equipment to handle the treatment of such liquids.
In the past, one solution to the removal of oils or low density solids within an inclined passage clarifier has required operation of the clarifier in an upflow mode with liquid to be clarified and the low density oils or solids being separated and removed at the top of the passages. Complete removal of the low density solids or liquids in such a mode of operation has been difficult because of what may be termed a "wiping" effect. Such as effect tends to occur in the final phases of removal where a large portion of the low density solids or liquids has been removed from the effluent. If the liquid to be clarified, in these final stages, is in close proximity to the low density solids or liquids being removed, there is a tendency for the liquid to pick up or retain a small portion of the low density liquids or solids. This effect is referred to as "wiping" and may occur if the liquid to be clarified is moving in either the same direction or the opposite direction from the low density liquids or solids.
Thus, there has been found to remain a need for a versatile inclined passage clarifier permitting the use of a single clarifier design or at least only a slightly modified design in a widely varying number of applications under different operating conditions.